It has been recognized for over twenty years that the kidney is able to escape from the antidiuretic effect of the hormone vasopressin (VP) following chronic VP administration. Since the mechanism underlying this escape phenomena has not been delineated, the objective of the present proposal is to determine the factor(s) responsible for development of renal resistance to the antidiuretic effect of chronic VP. There is substantial evidence that the 3',5' -cyclic adenosinemonophosphate (cAMP) system mediates in part the antidiuretic effect of VP. Thus, the role of the cAMP system in VP escape will be determined by analysis of adenylate cyclase, cAMP, phosphodiesterase and protein kinase in renal tissue removed in vivo from animal models of VP escape. If these studies indicate a role for the cAMP system in VP escape, then in vitro studies will be undertaken in renal tissue slices and isolated collecting ducts to determine the mechanism for cAMP system abnormalities. The potential role of VP-independent factors such as diminished renal medullary/papillary solute concentration in VP escape will be assessed by direct measurement of renal tissue solute from animal models of VP escape. If diminished tissue solute is found, the mechanism of this decrease will be examined by clearance techniques measuring glomerular filtration rate, total renal blood flow and renal papillary plasma flow and ascending limb of Henle function (maximum free water clearance and reabsorption studies). Substantial evidence suggests that VP stimulates renal prostaglandin (PG) synthesis and that PG's are capable of antagonizing the hydroosmotic effect of VP. Thus, a role of PG's in VP escape will be assessed by determining if VP escape is associated with increased renal PG production and by analyzing the effect of PG inhibition on VP escape. If these studies suggest a role for PG in VP escape, then studies will be performed to determine if PG exert their effect through a cAMP or tissue solute mechanism. These experiments utilizing whole animal metabolic balance studies, clearance techniques and in vivo and in vitro biochemical analyses will be complementary in clarifying the mechanism of VP escape.